When you are setting a task for repeating, it’s possible to set the frequency to ‘every 0 days’. It doesn’t really work properly (I would expect the task to repeat immediately after completion) if you set it up that way, and this is not possible to do on the desktop app.
If you set up a task to repeat every 0 days on mobile, on desktop the date when the task will be repeated shows as ‘invalid’.
Related to: Repeating tasks immediately after completing - #2 by Andrei